title: Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men.
abstract: BACKGROUND
  Sarcopenia has been attributed to a diminished muscle protein synthetic response to food intake. Differences in digestion and absorption kinetics of dietary protein, its amino acid composition, or both have been suggested to modulate postprandial muscle protein accretion.
  
  
  OBJECTIVE
  The objective was to compare protein digestion and absorption kinetics and subsequent postprandial muscle protein accretion after ingestion of whey, casein, and casein hydrolysate in healthy older adults.
  
  
  METHODS
  A total of 48 older men aged 74 ± 1 y (mean ± SEM) were randomly assigned to ingest a meal-like amount (20 g) of intrinsically l-[1-(13)C]phenylalanine-labeled whey, casein, or casein hydrolysate. Protein ingestion was combined with continuous intravenous l-[ring-(2)H(5)]phenylalanine infusion to assess in vivo digestion and absorption kinetics of dietary protein. Postprandial mixed muscle protein fractional synthetic rates (FSRs) were calculated from the ingested tracer.
  
  
  RESULTS
  The peak appearance rate of dietary protein-derived phenylalanine in the circulation was greater with whey and casein hydrolysate than with casein (P < 0.05). FSR values were higher after whey (0.15 ± 0.02%/h) than after casein (0.08 ± 0.01%/h; P < 0.01) and casein hydrolysate (0.10 ± 0.01%/h; P < 0.05) ingestion. A strong positive correlation (r = 0.66, P < 0.01) was observed between peak plasma leucine concentrations and postprandial FSR values.
  
  
  CONCLUSIONS
  Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. This effect is attributed to a combination of whey's faster digestion and absorption kinetics and higher leucine content. This trial was registered at clinicaltrials.gov as NCT00557388.
authors.affiliation: Top Institute Food & Nutrition, Wageningen, Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Pennings
authors.forename: Yves
authors.initials: Y
authors.lastname: Boirie
authors.forename: Joan M G
authors.initials: JM
authors.lastname: Senden
authors.forename: Annemie P
authors.initials: AP
authors.lastname: Gijsen
authors.forename: Harm
authors.initials: H
authors.lastname: Kuipers
authors.forename: Luc J C
authors.initials: LJ
authors.lastname: van Loon
mesh_terms: D000368:Aged; D000465:Algorithms; D001628:Beverages; D001707:Biopsy, Needle; D002364:Caseins / Q000737:chemistry / Q000627:therapeutic use; D004063:Digestion; D006801:Humans; D007408:Intestinal Absorption; D007700:Kinetics; D007930:Leucine / Q000032:analysis / Q000097:blood / Q000627:therapeutic use; D008297:Male; D008894:Milk Proteins / Q000737:chemistry / Q000627:therapeutic use*; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010649:Phenylalanine / Q000097:blood / Q000378:metabolism; D019518:Postprandial Period; D011492:Protein Hydrolysates / Q000737:chemistry / Q000627:therapeutic use; D055948:Sarcopenia / Q000178:diet therapy* / Q000378:metabolism; D000067816:Whey Proteins
chemical_list: D002364:Caseins; D008894:Milk Proteins; D009124:Muscle Proteins; D011492:Protein Hydrolysates; D000067816:Whey Proteins; D010649:Phenylalanine; C475729:casein hydrolysate; D007930:Leucine